Telephone system



Sept. 12, 1944. F. KEssLER TELEPHONE SYSTEM Filed Feb. 1',

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. l l 25A) I Gael) C282) ll VENTOR. FRANK KessLeR ATTORNEYS Sept 12, l944 F. KEssLER 2,358,013

TELEPHONE SYSTEM Filed Feb. 1, 1945 8 sheets-sheet 3 y FIRST TRUNK cIRcuIT FIRST GROUP 4| 35| LINE R3Io l 394 DIAL 316 v sLAvE R340 e211w cam cava INVENTOR. FRANK KESSLER AT 'roRIII-:Irs

F. KESSLER- TELEPHONE SYSTEM med Feb. 1, 194s B sheets-sheet r4 ATTORNEYS sept. 1,2, 1944.

F. KESSLER TELEPHONE SYSTEM Filed Feb. l, 1945 'moomms SELECTOR INCOMING sELeToR l LocKouT l CONNECTOR 8 Sheets-Sheet 5 OTHER GROUPS MARKER sa. seo

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IN V EN TOR.

FRANK KESSLR ATTORNEYS sept. 12, 1944. F'. KESSLER 2,358,013

` TELEPHONE SYSTEM Filed Feb. 1. 194s a sheets-sheet e FIG@ suf-H+ l POLAR cca-H7 f 6m suPvv "6 'iivmalo 627 53,

OPERATOR SWITCHBOARD 60o D|5TA-T EXCHANGE 30 CENTRAL oFrf'lcE lo Afro RNEYs Sept. 12, 1944. F. KEssLER 2,353,013

l TELEPHONE SYSTEM Filed Fb. 1, 1943 8 sheets-sheet v vFIRST TRUNk GIRGUI''V SECOND GROUP 5l4 "kT- v DIAL EAI R730 REV.

rss Y T 7.34 DIAL 1475 s'LAvE v r-r'r'r Y cssow cash eeen INVENTOR. FRANK KessLER BY l D 'm MQ/,M mi ,Y

ATTORNEYSl lSept'. 12, 1944.

F. KEssLER 2,358,013

TELEPHNE SYSTEM Filed Feb. 1, 1945 s sheets-sheet? f FRANK KESSLER ATTO RNEYS Patented Sept. 12, 1944 TELEPHONE SYSTEM Frank Kessler, Lombard, Ill., assigner to Automatic Electric Laboratories, Inc., a corporation of Delaware Application February 1, 1943, Serial No. 474,233

` 16 Claims. (01. 179-27) The present invention relates to telephone systems and more particularly to tandem switching systems.

A conventional telephone system of4 the type noted comprises a plurality of exchanges each i5 including an operator switchboard, a switching center including switching apparatus and terminating a plurality of lines, and a plurality of groups of trunks individually extending between the operator switchboards in the exchanges and l0 the switching apparatus in the switching center; wherein the switching apparatus is selectively controllable over the different trunks to complete both trunk-to-trunk calls and trunk-to-line calls. s

It is an object of the present invention to pro- T5 vide in a telephone system of the type noted improved switching apparatus in the form of switches individual to the trunks, whereby the two switches individual to calling and called trunks are operative to seize a common link in 520 order to set up a connection between the calling and called trunks. i

Another object of the invention is to provide in a telephone system of the typeA noted improved switching apparatus in the form of V25 switches individual to the trunks and switching mechanism common to the trunks, vwhereby the two switches individual to calling and called trunks are operative to Seize a commonlink in r, order to set up a' connection between the calling "30 and calledftrunks, and whereby the switching mechanism common to the Atrunks is controllable over a calling trunk to seize a called line in order to set up a connection between the calling trunk M and the called line independently of the switch 35 individual to the calling trunk.

vA further object of the invention is to provide in a telephone system including a line having a nder switch individual thereto, an improved ar- Y rangement for selectively controlling the oper- '740 ation of the iinder switch, whereby Vthe finder switch is operative to Set up both an outgoing call from the line and an incoming call to the line.

Further features of the invention pertain to the '45 particular arrangement of the circuit elements of the system, whereby the above-outlined and additional operating features are attained,

The invention, both as to its organzationand method of operation, together with further ob- `50 jects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings, in which Figure 1 illustrates the general the present invention; Figs. 2 to 8, inclusive, taken together, illustrate the details of a system having incorporated therein the features of the' invention as briefly outlined above; and Fig. 9 illustrates the mode of combining Figs. 2 to'8, inclusive, of the drawings to form a unified system.

Description of the apparatus incorporated inV the `system Referring now more particularly to Figfl `of the drawings, the telephone system there illustrated comprises a central voffice I0 of the automatic type and a plurality of distant exchanges 20, 30 etc. of any suitable type, the central oiiice l0 constituting a switching center for the system. The central oice lll and each of the distant exchanges are interconnected by a group'of trunks; the group of trunks interconnecting the central oihce I0 and the distant exchange 20, including the iirst trunk 43 and the last trunk 44, and the group of trunks interconnecting the central office I 0 and the distant eXchangeBll, including'the rst trunk 53 and the last trunk 54. Each of the distant exchanges comprises an operator switchboard of any suitable type terminating the group of trunks extending thereto; the operator switchboard 2| being provided in the distant exchange 20 and terminating the group oftrunks, including the trunks 43 and 44, and the operator switchboard 3l being provided in the distant exchange 30 and terminating-the groupv of trunks, including the trunks 53 and 54. K

Each trunk in e'ach group is terminatedin a trunk circuit individual thereto provided in the central ofiice l0; the first; and last trunks 43 and 44, respectively,v in the first group being provided with the iirst and last trunk circuits 4| and 42, respectively, in the first group and the first and last trunks 53 andY 54, respectively, in the second vgroup being provided with the iirst and last trunk circuits 5| and 52, respectively, in the second group. Also eachgroup of trunk circuits is provided with common equipment in the central office l0; the rst and lasi; trunk circuits 4| and 42, respectively, in the first group being provided with the common equipmentrst group 40 and the first and last trunk circuits 5| and 52, respectively, in the second group being provided; with the common equipment second group 50. Each of the trunk circuits comprises a iinder switch; the

rst trunk circuit first group 4|, the last trunk circuit first group`42, the rst trunk circuitsecond group 5| and the last trunk circuit second group 52 being respectivelyy provided with' the nder switchesGMF, 42F, 5|IiI and 52F. Alsoeach links, including the first link 6| and the last link 62; each link in the group being accessible to the.-

iinder switch of each trunk circuit in each group and being operatively associated with each trunk ually associated contact banks, and a magnet M8'56 for driving the wipers noted step by step in the clockwise direction. It will be understood that the last trunk circuit second group indicated in Fig, 6, will comprise similar equipment including a relay group, this relay group including the lockout relay RB60 illustrated.

Preferably, each common equipment is identical to the common equipment rst group lil individually associated with the trunk circuits in the iirst group and to the common equipment second group 50 individually associated with the circuit in each of the groups,` for a, purpose more.

fully explained hereinafter.V Further the central office I comprises switching apparatus, including not only the incoming selectors 45, 46, 55, 56 etc.

but a number of connectors 'Hf etc, of Vany suit- Vcircuit 14' of any suit'ablevtype'.

Preferably, each ofthe trunk circuits is identical. tothe first trunkV circuit :tlrstl group4;|. belminating-the first trunkfirst group. 43 extending between the-central office Illand. the-distant exchange 2-0, andl tothe: first Vtrunk circuit second group-| terminating the-first'trunky second group 5 3- extending between the central oflice.- |10,- an thedista-nt exchange 3u,

More particularly,Y theiirst trunk circuit rst group` 4,.|4 comprises,asshownfinEigs. 3 fand 4, a

relaygroup, includin a.` line relay RMD, a. hold relay- RSZl-a dial, relayfR, adial, slave relay .R340;,a, battery reverse.,relayellviSlt,V a, signalrelay 3360i: a. Supervisory-relay R310., a Signal: Slavefrielay R380, a lockout: relayfRAl ananswer relay R420-, alocal. relay Ruh a, sta-rt relay-124453,11 S1561? Telafy Rand at switch-throughrelay R450; Alsothefirst trunk circuit; first,group, 45| comprises arepeatingcoil. 39,!!1 and, a contr-01:2 network connectedgand arranged in` a. mannenmore fully explained-1.hereinafter, B urt-her ther ndenswitch MF individual to the r-sttrunlccircuit; rstgl'oxup 4| isof the rotary type, including; i'lve.y wipers-z 415| toA 415, inclusive, provided with', individually as.- sociated;v Contact banks.` antifa; magnetl M41 6T for driving thewipersncted stephy: stepinathe clock.- wise4 direction- It; will be understood. that, the lasttrunk l circuitrstgroupv 42.,` indicatecl'in; Fig. 2', will comprise similar equipment including a relay; group, this; relay;Y group including: the. lock:- out; relay R260 illustitefted.`

Similarly; the first Vtrunkcircuit; second group 5|- comprises, asjslcownini Figs. '7; and 8,. airelay group; including. a. line: relay? R110; a` holds relay IRI-12.11;. a, dialiI telaio R135; a; dial slave` relay R140, a; battery'y reverse relay R150,- a signal; relay RFI 51|,

a. supervisory relay: R110; a signa-la slave relay Rlsmalockcutfrelayfrtll I-0.=, an answer relayV R820, alccal relavRss a. ste-rt. relay:` R849.; a. sten ref lai? R85@ anda switch-through.relayRlO. Also ai, repeatingE coil-V 19.0 arldfaf.. control network connectedand,l arranged in;Y a.: manner more fully explained hereinalter; Further` thefnderfswitch The position` equipment provided at the operator trunk; circuits in the second group. More particularly, the common equipment first group 4!) comprises,A as sho-wn in Fig. 2, a relay group, includingtwo.timer'relays R230 and R235, a cutoff relay R240 and a step relay R250; andV a control. network connected and arranged in a manneprnorefully explained hereinafter. Similarly, the common equipment second group 5|! cornpriSeS; aSSllOWn inFig, 6, al relay group, including; two. timer1 relaysR|35 and R635,4 a cutoff relay R640 and a step relay'RS50; and a, control network connected andy arranged in a manner Inoue fully explaii-iecl;` hereinafter.

As, previously noted; each. operator switchboard cach; distant exchange,v is of any suitable type,

andr preferably the operator; switchboards. 2|, 3| eter., are identical. Each operator` switchboard corrugiri,SeilV position equipment. which may be op-.

eratiyely connectedl to the trunks extending tlficrtttc-f- The position equipment provided at the operator switchboard 2..| in.: the distant exchange 2p. is illustrated; in Fig; 2y asV beingy connected to .thefrstxtrunkY firstgroup,|33;and` as comprising a `repeating; coil' 200., a; Supervisory relay R-2|1||,'a signal relay;v R220.; aftalkkey K206i, a. dial 2.09,. a supervisory-l lampv 151204 an answer. lamp L2ll5. and a control-v IletWcrk connected and arranged in manner, more, ful-lyv explained hereinafter.

switchboard 3| in the distant exchangeis illustrated` in, Eig, 6i as; being connected'v tothe first trunksecondf group 53zanf1` ascomprising a repeatingcoil 69), a supervisory relay R613, a sig- Urlriflay R625, a talk key, KEES, a dial 609, a

Supel/isolfy lamp.L684,; an answer lampLBll5., and

a control network; connectedl and'arranged ina.

mannen more fully explained hereinafter.

Fig. 5 amarker switch 580 of theminor type, includinggtwowipers 58|` and 582 provided with individually associated contactbanks, a rotary ,magnet M583 -fordriving. the' wipers noted step by step in the counterclockwise direction, and a release magnet lvl-58.1 for releasing the wipers noted. and:V flor: causing them to. be returned to them normal* rota-ry positions. Alsoy associated With the marker switch 580 is aset of switch springs: S584; which is actuated when the wipers noted; are; operated two steps away fromy their normal rotary positions.

R5|0., a pulse relay R520, a hold relayl R530', a dial rela-y R540.; a cutoff; relay R550 and a release relayy 135503:? and a control network connected group includ-ing thel lockout. relay R510 illus- Plefelably, each of' the links is identical to. the' llrst-`link B'llwhich comprises, as shown vin Also the rst link. 6| 'Y comprises a relay group, including a lockout relay Y Initiation of a call in a distant archange Considering now the initiation of a call at an operator switchboard in a distant exchange, such, for example, as the operator switchboard 2| in the distant exchange 20, the operator at the switchboard 2| rst selects an idle trunk in the group terminated thereat and connects the asi sociated position equipment thereto. For example, the operator at the switchboard 2| may select the rst trunk rst group 43 and connect the associated position equipment thereto, as illustrated. Next, the operator at the switchboard 2| operates the talk key H206 individual to the rst trunk firstgroup 43, whereby there is completed, at the contacts 201 thereof, a series circuit for energizing the winding of the supervisory relay R2 I0 inthe associated position equipment and the upper and lower windings of the line relay R3|0 in the first trunk circuit rst group 4| via the rst trunk rst group 43. The above-mentioned circuit extends from ground by way of the lower winding of R3|0, the. contacts 353 and 36|; the winding 392 of the repeating coil 396, the line conductor C212 of the rst trunk 43, the dial 209, the winding 202 of the repeating coil 200, the contacts 201 of the talk key K205, the winding of the supervisory relay RZIQ, the winding of the repeating coil 200, the line conductor C21| of the rst trunk 43, the winding 39| of the repeating coil 390, the contacts and the upper winding of R3|0 to battery. When the above-traced series circuit is completed the supervisory relay R2|0 in the position equipment at the operator switchboard 2| does not operate as it is of the polarized type, while the line relay R3 I 0 in the i'lrst trunk circuit 4| operates.

Upon operating, the line relay R3|0 completes, at the contacts 3|2, an obvious circuit for energizing the winding of the hold relay R320, thereby to cause the latter relay to operate. Upon operating, the hold relay R320 completes, at the contacts 322, a circuit,` including the contacts 455 and 465, for energizing the winding of the start relay R440, thereby to cause the latter relay to operate. Upon operating, the start relay R440 first completes, at the contacts 44|, and then interrupts, at the contacts 442, a circuit, including the contacts 465, 4|5 and 322, for energizing the magnet M416 of the under switch 4|F, whereby the latter magnet operates and restores. Upon operating, the magnet M416 conditions the wipers noted of the finder switch 4|F to be driven one step in the clockwise direction; and, upon restoring, the magnet M416 drives the wipers noted one step in the clockwise direction. Also the start relay R440 interrupts, at the contacts 441, a normally completed connection, including the contacts 463', 436 and 4|3, between the rst marking conductor C50| and the winding of the 'lockout relay R4|0, thereby to mark the iirst trunk circuit 4| in the rst group as busy to the marker switches of the various links. Also the start relay R440 completes, at the contacts.

446, an obvious connection, including the contacts 463', between the rst marking conductor C50| and the chain conductor C423 extending to the second trunk circuit in the rst group, thereby to render the second trunk circuit in the first group selectable by the marker switches of the various links, Further the start relay R440 completes, at the contacts 443-and 448, a test connection between the winding of the switch-through relay R460 and the control wiper 414 of the nder switch 4|F. At this time the wipers noted of the finder switch 4|F engage the conductors extending to one of the links 6|, 62 etc. and thelink mentioned is either idle or busy and the idle or busy condition thereof is ,tested by the switch-through relay R460 in the first trunk circuit 4|. More particularly, in the event the engaged link is respectively busy or idle, ground potential or no potenti'a1 is respectively connected to the control wiper 414 of the finder switch 4 IF.

Assuming that the engaged link is busy, ground potential appears upon the control conductor thereof and is connected to the control wiper 414 of the nder switch 4|F, thereby to completer a path, including the contacts 316, 4|9, 461, 443, 431 and 448, for short-circuiting the winding of the switch-through relay R460 in order positively to prevent operation of the latter relay at this time. Also the application of ground potential to the control wiper A414 of the finder switch 4| F completes a circuit, including the contacts 316, 4I9, Y

461, 443, 4|8 and 411, for energizing the magnet M416, thereby to cause the latter magnet to operate. Upon operating, the magnet M416 conditions the wipers noted of the finder switch 4 IF to be driven an additional step in the clockwise direction and interrupts, at the contacts 411, the

previously traced circuit for energizing the magnet M416, whereby the latter magnet restores. Upon restoring, the magnet M416 drives the wipers noted of the iinder switch 4|?1 an addi"- tiona-l step in the clockwise direction tc engage the conductors extending to the next link 6|, 62

etc., whereby the idle or busy condition thereof is tested in the manner explained above. iAccordingly, the magnet M416 operates intermittently, thereby to drive the wipers noted of the finder switch 4|F step byrstep in the clockwise direction until an idle link 6|, 62 etc. is tested by the switch-through relay R460 in the rstk trunk circuit 4 l.

Assuming that the vfirst link 6| illustrated is the rst idle link tested by the switch-through relay R460 in the rst trunk circuit 4|, when the wipers noted of the nder switch 4|F engage the conductors 048| to C485, inclusive, extending to the rst link 6|, no ground potential appears upon the control conductor C484 in View of the fact that the hold relay R530 in the rst link 6| occupies its restored position. At this time, no ground potential appears upon the control conductor C484 and consequently upon the control wiper 414 of the nder switch 4|F, whereby the previously traced path for short-circuiting the winding of the switch-through relay R460 in the rst trunk circuit 4| is not completed. At this time, a series circuit is completed for energizing the winding of the switch-through relay R460 and the magnet M416 this circuit extending from ground-by way of the contacts 448, the winding of R460, the contacts 431, 4|8 and 411 and the magnet M416 to battery. When this series circuit is completed the switch-through relay R460 operates; however, the magnet M416 does not oping of the switch-through relay R460.

Upon operating, the switch-.through relay R460 completes, atthecontacts l464l and 46,6, anl alternati-vey holding, circuit,` including, the contacts 322, 43,1, 4|,8, andl411', for energizingthe windingthereofv in series with the magnet M4161; interrupts, at the contacts;46:1, aiur,ther point in the previously traced circuit, including the, control wiper- 414l of the iinder, switch MF, for yenergizing thel magnet M416. Also the switch-through relay R460 completes, atthecontacts 4,64, 466 and 468, an` obvious path, including theA contacts 3,-22, 4|9 and 316:, rior applying ground potential to the control wiper 414- of the nder switch 4|E,1 and consequently to the control conductor C484, extending tothe first link 6|. This application of ground potential to the control conductor C484 extending-to, the first link 6| marks the first link 6| as busy to the, other finderA switches in the various Y groups having access thereto, as previously explained. Further the switch-through relay R460 V interrupts, atv the contacts V463.', the previously traced path, including the contacts 446, between the first marking lconductor C501 and the, Chain conductor C423; and completes, at the contacts 462', an obvious alternative connectionV between theiirst marking conductor` C50| and the,` chain conductor C423, thereby to. maintain the second trunkfcircuit in the first group selectable by the marker switches ofthe various links. Further theV switch-.through relay R460 completes, at the contacts 46|', an obviousipath, including the contacts 445for applyingground potential to the control wiper 4,15 ci the nder switch 4|F.` Further, theswitch-through relay R460 interrupts, atv the contacts-465, the previously traced circuit for energizing the winding of the start' relay R440, thereby to cause the latter relay to restore. Finally the switch-through relay R450 completes', at the contacts 46| and 462, obvious connections between the windings 393 and 304 of the repeating coil 300! and the' line wipers 41| and 412 of the 'nder'switchMF, for a. purpose moreY fully explained hereinafter. r

Upon restoring, the 'start relay R440V interrupts, at the contacts 445., the previously traced path for applying ground potential to the -control Wiperf415 of the nder switch 4|F and cornpletes, at the contacts 444, an obvious circuit,l inciludingv the contacts 469, for` energizing the winding of the step relay R450, whereupon the latter relay operates shortly thereafter, the step relay R450 being of the slow-to-operate type.V

Upon. operating, the step relay R450 completes, at the contacts 45|, an alternative path, including the contacts 3|4, 31,1" and 46|', for applying groundl potential to the control wiper 41=5 of the finder switch 4|F. Accordingly, ground poten- V'R520 operates, restores and then reoperates, in

an obvious manner. Upon operating; the pulse relay R520 completes, at the contacts 52|, an obvious circuit for energizing the winding of the hold relay R530, thereby to cause the latter relay to operate. Upon restoring, the pulse relay R520 interrupts, at the contacts 52|, the

previously mentioned, circuit for energizing.. the 'winding of the hold relay R530; however, the latter relay does not restorer during; the impulse as it is of the slow-to-release type. Also, upon restoringthetpulse relay R520 completes, at the contacts` 522, an obviousY circuit, includingy the contacts 534 and the contacts 585 of thev set of; switch springs S584, for energizing in multiple the winding of the dial relay R540- and the rotary magnet M583, whereby the dial relay R540 and the-rotary magnet M583=operate.y Uponoperating, the rotaryl magnet'M583 drives the wipersY noted of the marker switch 580 one step inf the Y counterclockwise direction. Upon operating, the

dial relay R540 prepares, at the contacts 54|, a

circuit for energizingthe winding of thelockout relay R5|0; which circuit YVis completed in the event the lockout relays in all of the links occupy their restored positions at'this time. Assuming that the lockout relays in all of the links occupy their restored positions at this time, the circuit for energizing the winding of the lockout relay R5| 0 in the first link 6| is completed and extends from ground by way of the contacts 54| and 53|', the winding of REID, the contacts 5|2, the contacts of the other lockout relays, the contacts 5|3 and the resistor 565 to battery. When thus energized the lockout relay R5|0 operates tov complete, at the contacts 5| an obvious holding circuit for energizing the windingr thereof, and to interrupt, at the contacts 5|,2,` a point in the previously, traced original cir-cuit for ener` gizing the winding thereof. Also the lockout relay R5|0 interrupts,- at the contacts 5|3, a common point in the circuits for energizing the windingsof the lockout. relays inthe other links, thereby positively to prevent operation of the other lockout` relays at4 this time. When the pulse relay R520 reoperates it interrupts, at the contacts 522, the previously traced circuit vfor energizing in multiple,thewin'dingY of the dial relay R540 and the rotary magnet M583, whereby thef rotary magnet M583 restores immediately and the dial relay R540 restores shortly thereafter, the dial relay R540 being of the slow--to-V release type. YUpon restoring, the dial relay R540 completes, at the contacts 544, an obviousalternative holding circuit, including the contacts 563, the Wiper 582L of the marker switch 580 and the engaged rst contact in the associated contact bank, the contacts 53| and 5|| and the resistor 565, `for energizing ther windingy of the lockout relay R5I-0. Also the dialY relay R540 interrupts, at the contacts 54|, the previously traced original holding circuit for energizing the winding of the lockout relay R5|.0. Accordingly, at this time, the pulse relay R520, the holdrelay R530 and the lockout relay R5|0 in the iirst link 6| occupy their operated positions; the lockout relays in the other links are positively retained in their restored positions; and the first link 6| is in readiness to receive a digit dialed over the connected finder switch 4|F of the first trunk circuit 4| via the first trunk 43 at the operator switchboard 2| in the distant exchange 20; Accordingly, at this time, the position equipment at the operator switchboard 2| in the distant exchange 20 is operatively connectedV to the first link 6|` and the operator at the operator switchboard 2| may proceed with the settingy up of the connection either to a called subscriber substation in the central oiiice |0,` or to a called operator switchboard in one of the distant exchanges 30, etc., as explained more fully below.

Completion of a callto a subscriber substation in the central office Now assume that the call initiated at the operator switchboard 2| in the distant exchange 20 and extended via the rst trunk first group 43, the rst trunk circuit rst group 4| and the finder switch 4|F individual to the first trunk circuit 4l to the first link 0| is to be completed to a subscriber substation in the central office l0, such, for example, as the subscriber substation T. In this event, the operator at the switchboard 2| in vthe distant exchange 20 rst proceeds to dial the corresponding group digit for the central ofce I0, such, for example, as the digit 9 at the dial 209. The impulses of the digit 9 are transmitted from the dial 209 at the operator switchboard'Zl over the rst trunk 43 to the line relay R3|0 in the first trunk circuit 4|, in an obvious manner, whereby the line relay R3|0 follows the impulses of the digit mentioned and repeats them, at the contacts 3|4, in the form of ground impulses to the control wiper 415 olf the finder switch 4|F. More particularly, each time the line relay R3|0 restores and then reoperates it interrupts and then recompletes, at the contacts 3|4, the previously traced circuit, including the contacts 311, 45| and 40|', the control wiper 415 ofthe nder switch 4|F and the engaged contact in the associated contact bankand the control conductor C485, for energizing the winding of the pulse relay R520 inthe first link 6|, whereby the pulse relay R520 restores and then reoperates. Accordingly, at this time, the pulse relay R520 restores and reoperates nine times in accordance with the digit 9. The first time the pulse relay R520 restores and then reoperates it completes and then interrupts, at the contacts 522, the previously traced circuit, including the contacts 534 and the contacts 585 of the set of switch springs S584, for energizing in multiple the winding ofthe dial relay R540 and the rotary magnet M583, whereby the dial relay R540 and the rotary magnet M583 reoperate. Upon reoperating, the dial relay R540 completes, at the contacts 543, an obvious path in multiple with the contacts 585 of the set of switch springs S584. When the wipers noted of the marker switch 580 are driven two steps in the counter clockwise direction away from their normal rotary positions, the set of switch springs S584 is actuated, thereby to interrupt, at the contacts 585 thereof, a point in the previously traced original circuit for energizing in multiple the winding of the dial relay R540 and the rotary magnet M583, and to prepare, at the contacts 585 thereof, a point in a circuit traced hereinafter :for energizing the release magnet M581. The hold relay R530 and the dial relay R540 remain operated during impulsing Aas both of these relays are of the slow-to-release type, as previously noted. Accordingly, at the conclusion of the Ydigit 9, the wipers noted of the marker switch 580 engage the tenth contacts in the associated contact banks; the pulse relay R520 and the hold relay R530 are retained in their operated positions; and, shortlyT thereafter, the dial relay R540`restores.

Upon restoring, the dial relay R540 interrupts, at the contacts 54|, the previously traced original holding circuit for energizing the winding of the lockout relay R|0, vwhereby the latter relay restores at this time. Upon restoring, the lockout relay R5|0 reprepares, at the contacts 5|3, the common point in the circuits for energizing the ofthe finder switch ,4|F. Also the restoration4 andreoperationof the line relay R3|0following the impulses ofthe digit` 9 repeat the impulses thereof, at the contacts 3| l, by way of the contacts 32| to the winding oif the dial relay R330 in the rst trunk circuit 4|. Further each time the line relay R3|0 restores and then reoperates it interrupts and then recompletes, at the contacts 3|2, the previously traced circuit for energizing the winding of the hold relay R320. The hold relay R320 and the dial relay R330, both being of the slow-to-release type, remain operated during impulsing; and, at the conclusion of the ldigit 9, the line relay R310 and the hold relay R320 remain operated and the dial relay AR330 restores shortly thereafter. Upon operating, the dial relay R330 completes, at the contacts 334, an4 obvious circuit for energizing the winding of the dial slave relay R340, thereby to cause the latter relay to operate.

Shortly following the-conclusion of the digit 9 the dial relay R330 restores, as previously noted, thereby to complete, at the contacts 333, a circuit forenergizing the winding of the local relay R430. The last-mentioned circuit extends from the grounded wiper 413 o f the finder switch 4|F by way of the contacts 4|2v, 333, 34| and 463 and the winding of R430 to battery. `When thus' energized the local relay R430 operates to complete,

at-the contacts 436, an obvious holding circuit, K

including the contacts 322,- for energizing the winding thereof. Also, upon restoring, the dial relay R330 interrupts, at the contacts 334, the previously mentioned circuitifor energizing the .winding of the dial slave relay R340, thereby to cause the latter relay to restore shortly thereafter, the dial slave relay R340 beingof the slowto-release type. Upon restoring, the dial slave relay R340 interrupts, at ythe contacts 34|, the previously traced connection between the winding of'the local relay R430 and the controlwiper 413 of the finder switch 4 I F.

Also, upon operating, the local relay R430 interrupts, at the contacts 431, the previously traced holding circuit for energizing the winding vof` the switch-through relay R460 in series with the magnet M416, thereby to cause the switchthrough relay R460 to restore. Also the local yrelay R430 interrupts, at the ,contacts 439, a further'point in the previously traced` connection between therst marking conductor C50| and the winding ofthe lockout relay R4|0, and prepares, at the contacts 438, a point in' an alternative connection traced hereinafter between the rst marking conductor (250| andthe chain .condufctor C423. Furtherv the local relay R430 completes, at the contacts '43|, 432 and 435, a bridge connection including the winding of the answer relay R420 between the line, conductorsof the trunk 41 extending to the incoming selector 45 individual to the first trunk circuit l4|.V The above-mentioned bridge connection extends from one of the line conductors of the trunk 41 by way of the contacts 43|, the Winding 393 of the repeating coi1390, the contacts 435, the winding of theanswer relay R420, the contacts3l3', the

winding 3,94 ofthe repeatingcoil 390 and the Y digitoverthe trunk 41 thereto.

' answer relay R420 does not operate at this time contacts V,4;32 to the .other line conductor of` the trunk 41. When Athe above-traced bridge :circuit isV completed thefwi-nding of ythev answer relay R420 is energized and the incoming selector '45 is rendered responsive to the transmission of a However, the

as itis of the polarized type.

Upon restoring, the switch-through relay R460 interrupts, at the contacts 469, the vpreviously traced circuit for energizingithe winding of the steprelay R450, thereby to cause the latter relay to restore. Also the switch-through relay R460 interrupts, atV the contacts 462', the previously traced'alternative connection lbetween the first marking conducto-r (250| and the chain conductor C423, andgcornpletes, at the contacts 463', the

previouslymentioned'alternative connection including thellcentacts 441 and 43B between the -rst marking conductor 'C501 and-the chain conl cuit, including the contacts-52'2--and the VVcontacts 586 of the set ofswitch springs S584, for energizing the release magnet MWL-whereby the Vlatter magnet operates and releases the -wipers'noted of the marker switch 580, whereby the'wipers thereof are returned to theirnormal :rotary positions. When themarker switch 580 is thus'revthereby tointerrupt, at the contacts 586 thereof, the previously traced circuit 'for venergizing the release magnet M581, whereupon the lattermagnet restores. VA`1fso,upon restoring,-the'hold'relay R530 interrupts,A at the contacts 533,- theprevito the controllconductorl C484, thereby Lto' `mark the rst link 6| as idle tothe Vfinder switches of the various trunkcircuits'having accessthereto.

At't'his time, the first linkv 5| iscompletely'released and available for Ifurther use.

At this time the operator switchboard `2| is connected by way-of 'the rst trunk 43 to the first trunk --circuit'4l and the first trunk circuit is connected by way of the'trunk l41fto the incoming selector '45, as previously noted. `The operator at the operator switchboard 2| "then proceedsto dial the directory number of the leased the -set of switch springs S584 is actuated,

eusly traced path for applyin'gqgr'oundpotential Y acca-ola the s'ul scri`ber line extending to the cal-led subscriber substation The connector 1g| then operates in order to test the idle Aor busy condition `of the calledr subscriber substation T, whereby busy tone ris returned over the incoming selector 45 and the trunk 41in the `event the called subscribersubstation T is busy; andringing Vcurrent isprojected overthe subscriber line'13 to the called subscriber substation T and ring-back tone current isretur-ned over the incoming selector145" and the trunk 41 inthe event the called subscriber substation T is idle. The tone current returned over the trunk 41. traverses the Windings 393 and 394 of the repeating `coil 390 and the condenser 395 and inducescorresponding tone current in the windings `39| and 392 of the repeating coil 390 which traverses'the condenser -39.5, the rst trunk 43 and the windings 20| and 202 of therepeating coil 200 and the condenser 203. The tone current traversing .theV windings V20| and 202 of the repeating coil 200 causes tone current to traverse the telephone instrumentat the operator switchboard` 2|, in an obvious manner. Y K

Assuming that the called subscriber substation T is idle, ringing current is projected over the subscriber line 13 thereto and the linecircuit 14 lis controlled inorder to mark the subscriber line 13 Y as busy tothe other connectors having access thereto. When the subscriberat the called subscriber substation T vanswers 'thev call the con-- nector 1| operates in order to cause battery potential to be reversed over the'incoming selector 45 and the trunk 41, whereby the windingV `o` f the answer relay R420 is ,energizedintheopposite direction in `orderto `cause the latterrelay Y to operate. Upon operating, the answer relay R420 completes, at the contacts 42|, an obvious circuit for energizing the windingof the battery reverse relay R350, thereby tg` vcause the latter relay to operate. Upon operating, vthe battery reverse relay R350 interrupts, at the contacts 35| and 353, the previously traced loop circuit extending between the supervisory relay R210 at the'operator switchboardv 2| and thelinerelay R3|0 in the rst trunk circuit 4|, and recompletes, at the contacts 352 and 35,4, an obvious alternative loop circuit Ibetween the supervisoryI relay R2 I0 and the line relay R3 Ill; wherebybattery potential is reversed 'over the lineconductors of the iirst trunk 43 in order tol causethe winding fof the supervisory relay R2|0 to be energizedv in the opposite direction. The supervisory relay R2|0 then operates to complete, at'the contacts 2| l', an obvious'circuit for illuminating the superl visory lamp L254, thereby to indicate to the called subscriber substation T in the centraloice 1 I8; which directory number fcomprises three digits. The'thre'e digits'are -dialedatthe dial 209 at the operator-switchboard 4Zilrand are-transmitted over the rstft-runk 43 tothe line` relay R3|0 in. the-'first trunk circuit 4| ;V which line relayre-` Ypeats the impulsesof` the threedi-gits mentioned,

at the contacts.3|3, over the trunk 41V to the incoming selector-'45m -an-obvious manner; VTheV y incoming selector-v 45 responds Ytothe first digit mentioned to select a corresponding group of trunks and then operates automatically to select an idle trunk in the previously selected group. For example,V the incomingj selector 45l may operate toV select the trunk12 extending to the 'conhector 1|, assuming that-the con-nector 1| is idle at this time. The connector 1| then responds to the second andthirddigits mentioned to select operator at the switchboard 2 that the subscriber at 'the called subscriber substation TinV the central unice im has answered me can; At this time an established connection lsfcompleted. between theca'lling operator switchboard 2| in the distant exchange 20 `and the called subscriber substation 'I' in the central office 'I0 'this connection including the previouslytraced loop circuit betweenv therepeating coil 200 and the repeating coil 390; and the previously traced bridge circuit |between thev repeating coil 390 and th'econvnector 1|; the connector 1| being connected by way of the subscriber line 1310 the calledsubscriber substation TI V- Subsequently, 'in' the event'- the release vof 'the established 'connection is initiated 'by the sub- I 1 scriber. at the called subscriber` substation' T, when lthe subscriber thereat replaces the'receiver of thek telephone instrument upon its associated switchhook the connector 1| operates in order again to reverse battery potential over the incoming selector 45 and the trunk 41, whereby the answer relay R420 restores. Upon restoring, the answer relay R420 interrupts, at the contacts 42|, the previously mentioned circuit for energizing the winding of the battery reverse relay R350, thereby to cause the latter relay to restore and reverse battery potential over the rst trunk 43, whereupon the supervisory relay R2|0 restores. Upon restoring, the supervisory relay R2|0 interrupts, at the contacts 2| I, the previously mentioned circuit for illuminating the supervisory lamp L204, thereby to indicate to the operator at the switchboard 2| that the release of the established connection has been initiated at the called subscriber substation T in the central office |0.

The operator at the switchboard 2| then effects the further release of the established connection by restoring, the talk key K205, thereby to interrupt, at the contacts 201 thereof, the previously traced loop circuit for energizing in series the upper and lower windings of the line relay R3|0, whereupon the latter relay restores. Upon restoring, the line relay R3|0 interrupts, at the contacts 3|2, the previously mentioned circuit for energizing the winding of the hold relay R320, thereby to cause the latter relay to restore shortly thereafter. Upon restoring, the hold relay R320 interrupts, at the contacts 322, the previously traced holding circuit for energizing the winding of the local relay R430, thereby to cause the latter relay to restore. Upon restoring, the local relayR430 interrupts, at the contacts 43| and ,432, the previously traced bridge circuit between the repeating coil 390 and the connector 1|, whereby the -connector 1| is released in order to effect the release of the incoming selector 45. When the connector 1| is thus released the line circuit 14 is operated in order to mark the subscriber line 13 as idle, assuming that the subscriber at the called subscriber substation T has replaced the receiver of the telephone instrument upon its associated switchhook at this time. At this time the rst trunk 43 is disengaged and the rst trunk circuit 4| is marked as idle to the rmarker switches of the various links having access thereto. More particularly, upon restoring, -the local call relay R430 interrupts, at the contacts 438, the previously traced connection between the iirst marking conductor C5| and the chain conductor C423, and recompletes, at the contacts 439, the normal connection between the i'lrst marking conductor C50! and the winding of the lockout relay R4H), rendering the rst trunk circuit 4| selectable via the first marking conductor C50! to the marker switches of the various links. v

In view of the foregoing explanation of the mode of operation of the first trunk circuit first group '4| in conjunction with the firstlink 6| to extend a connection from the operator switchboard 2i in the distant exchange 20 via the first trunk rst group 43, the trunk 41, the incoming selector 45 individual to the iirst trunk circuit 4| and the connector 1| to the called subscriber substation T in the central cnice I0, it will be understood that the other trunk circuits in the `rst group are operative in a similar manner in conjunction with any one of the links to extend a connection from the operator switchboard 2| in the distant exchange 20 via the associated trunk Vin therst group, the trunk extending to the individually associated incoming selector, the

last-mentioned incoming selector and the connector 1| to the called subscriber substation T. Similarly, the other trunk circuits in the other groups are operative in conjunction with any one of the links to extend a connection from the operator switchboard in the corresponding distant exchange via the associated trunk in the corresponding group, the trunk extending to the individually associated incoming selector, the -lastmentioned incoming selector, and the connector 1| to the called subscriber substation T.

Completion of a call to an operator switchboard Y in a distant exchange Now assume that the call initiated at the operator switchboard 2| in the distant exchange 20 and extended via the nrst trunk first group 43, the nrst trunk circuit iirst group 4| and the finder switch 4|F individual to the first trunk circuit 4| to the first link 6| is to be completed to an operator switchboard in one of the distant exchanges, such, for example, as the operator switchboard 3| in the distant exchange 30. In this event, the operator at the switchboard 2| in the distant exchange 20 first proceeds to dial the corresponding group digit for the distant exchange 30, such, for example, as the digit 2 at the dial 233. transmitted from the dial 209 at the operator switchboard 2| over the rst trunk 43 to the line relay R3|0 in the rst trunk circuit 4|, in an obvious manner, whereby the line relay R3 0 follows the impulses of the digit mentioned and repeats them, at the contacts 3|4, in the form of ground impulses to the control wiper 415 of the finder switch 4|F. More particularly, each time the line relay R3| 0 restores and then reoperates it interrupts and then recompletes, at

the contacts 3|4, the previously traced circuit for energizing the winding of the pulse relay R520 in the rst link 6|, whereby the pulse relay R520 follows the two impulses of the group digit 2. In the present example, the pulse relay R520 restores and then reoperates twice, whereby the dial relay R540 is reoperated and the rotary magnet M503 is operated andv restored twice in order to drive the wipers noted of the marker switch 530 two additional steps in the counterclockwise direction and into engagement with the third contacts in the associated contact banks. When the wipers noted of the marker switch 580 are driven two steps away from their normal rotary positions the set of switch springs S584 is actuated, as previously explained.

At the conclusion of the group digit 2, the pulse relay R520 and the hold relay R530 remain in their operated positions and, shortly thereafter, the dial relay R540 restores. Upon restoring, the dial relay R540 interrupts, at the contacts 543, the previously traced multiple circuit for energizing the winding thereof and the rotary magnet M583, thereby positively to prevent further Voperation of the markerA switch 580 in view of the fact that the set of switch springs S584 is operated at this time. Alsoythe dial relay R540 interrupts, at the contacts 54|, the previously traced original holding circuit for energizing the winding of the lockout relay R5|0 and recompletes, at the contacts 544, the previously traced alternative holding circuit for energizing the winding of the lockout relay R5|0. Further the dial relay `R540 completes, at the ,contacts 542, a circuit, including the contacts 553 and 5|4, for applying ground potential by Way of the upper winding of The impulses of the digit 2 are gizing the winding thereof. Ylay R818 interrupts, at the contacts 818', -a comthe cutoff relay vR550 to the wiper 581 'of the markerswitch 580 and the engaged third contact in the associated contact 'bank and consequently tothe second marking conductor C502. The second marking conductor C502 vextends to the rst trunk circuit second group and is normally connected Yto the winding of the lockout relay R810 in Vtheiirst trunk circuit 51 in the event the last-mentioned trunk circuit is idle at this time.

the second marking conductor C582 is connected to the chain conductor C823 due to the operated position of one of the relays in the iirst trunk More particularly, the second markf circuit 51V. I ing conductor C502 is adapted to be connected to the chain conductor C823 bythe local relay R830,

'the start relay R849 cr the switch-through relay 'R860 under the conditions previously discussed in conjunction with the operation of the iirst f Vond group 5-1 is idle at this time, the application of resistance ground potential to theV second marking conductorY C502 completes a circuit for energizing the winding of the lockout relay R810. The last-mentioned circuit extends from theV grounded second' marking conductor C502 by way of the contacts 863', 841, 838 and 813', the winding of R810, the contacts 811', C680, the contacts of the lockout relays in the other trunk circuits,

C681, the contacts 81'8'Yand the resistor 822 to battery. When thus energized the lockout relay R810 operates `to interrupt, at the contacts 813' and 811', points in the previously traced original circuit for energizing the winding thereoiand completes, at the contacts 816 and 812', a holding circuit, including the contacts 631, 642, the conductor C611 -and the resistor 822, `for ener- Also the lockout remon point in the circuits for energizing the Vwindings of the lockout relays in the other trunkvcircuits inthe second group, thereby positively to prevent'operation of the lockout relays in the other trunk circuits in the secondr group at this time. Also the lockout relay R810 completes, at

the contacts 811', an obvious circuit, including the conductor C616, for energizing the winding ofthe timer relay R635 in the common equipment `second group 50 in order to cause the latter relay Yto operate.` Upon operating, the timer relay R635 sets its armature into vibration, whereby there is completed intermittently at the contacts 631-an ,obviou'scircuit including the contacts 811 and -the conductor C616, for energizing the `winding of the timer relay R630, wherebythe latter relay -isenergized intermittently. Howevergthe timer relay R630 isV of the islow-to-operate type and does not operate until aftera predetermined time intervaL-'for a purpose morefully explainedhereinafter. Y

Further Ythe lockout relay R810 completes, Yat the contacts 819', a path, including the conductor C682, for applying battery potential by way-of Vthe s resistor v653 -to the second marking Vconductor C502, thereby to complete a low resistance circuit :substantially identical to that previously traced On the other hand, Vin the event the iirst trunk circuit second groupr51 is busy at this time,

for energizing the upper Winding of the cutoi relay R550 in the rst link 61. AWhen thus energized the cutoff relay R550 operates to complete, at the contacts 554, an obvious holding circuit, including the contacts 563, for energizing ythe lower winding thereof, and to interrupt, at the contacts 553, the previously traced original path for applying resistance ground potential to the second marking conductor C502. Also the cutoff relay R550 completes, at the contacts 552, an obvious path, including the contacts 561, for applying battery potential by way of the upper` winding of vthe release relay R560 to the control conductor C483,` for apurpose more fully explained hereinafter'. Also at this point it is noted that the operated hold relay R530 retains com# 651 and the conductor C618, for energizing themagnet M816, thereby to cause the latter magnet to operate and conditionthe wipers noted of the nder switch 5IF individual to the rst trunk circuit second group 51 to be driven one step in the clockwise direction. Also theA magnet M816, upon operating, completes, `at the contactsr1818,

'an obvious circuit, including the contacts 816 and the conductor C614, for energizing the Winding of the step relay R650 in 'the commonequipment second group 50. When thus energized the step relay R650 operates to interrupt, at the, contacts 651, the previously traced circuit for energizing the lmagnet' M816, therebyto cause the latter magnet to restore and drive the wipers noted of the finder switch 51F one step in the clockwise direction. Also, -upon restoring, the magnet YM8115 interrupts, at the contacts A818, the previ'-V ously traced circuit for energizing `the winding of the step'relay R650, thereby toV cause the latter relay to restore and reprepare, at the contacts 651, the previously traced vcircuit for energizing the magnet M816. Accordingly, it Will-be understood that the magnet M016 and the step relay Y R650 interact, inthe manner described above,k

whereby the wipers notednof rthe finder switch 51E' are driven step by step inthe clockwise direction until they engage the contacts in the associated contact banks terminating the conductors extending to the first link' 61, which conductors are also terminated bythe contacts Aengaged by the wipers noted ofthe iinder switch 41F individual to the Yfirst trunk circuit rst group 41, the conductors mentioned being the conductors C481, C482, C483, C484 and C485 extending to therst link 61?.

More particularly, when iinder switch-5`1F engage the contacts in the associated contact banks terminating the conduce tors C481 to C485, inclusive, a Yseries Ycircuit is completed for energizing the upper winding of the wipers notedeofthe' ciated contact bank, C483,`the contacts 552 and 56I and-the upper winding of R 560 to battery. When this series circuit is completed the cutoff relay R640 and the release relay R560 operate. Upon operating, the cutoff relay R640 completes, at the contacts 64I, an obvious circuit, including the contacts 636, for energizing the lower winding thereof; and, upon operating, the release relay R560 completes, at the contacts 562, an obvious path for short-circuiting the resistor 564 and consequently an obvious holding circuit for energizing the lower winding thereof. Also the release relay R560 interrupts, at the contacts 56 I, the previously traced path for applying resistance battery potential by way of the upper winding thereof to the control conductor C483, and interrupts, at the contacts 563, the previously traced holding circuit for energizing the lower winding of the cutoi relay R550 and the previously traced multiple holding circuit for energizing the winding of the lockout relay R I 0, whereupon the cutoif relay R550 and the lockout relay R5I0 restore.

`Upon restoring, the lockout relay R5I0 recompletes, at the contacts 5I3, the common point in the circuits for energizing the windings of the lockout relays in the other links, whereby the other links in the group may be utilized at'this time. However, it is noted that the pulse relay R520 and the hold relay R530 are retained in v their operated position, thereby to retain busy the first link 6|. More particularly, the operated hold relay R530 retains completed, at the contacts 533, the previously mentioned path for applying ground potential to the control conductor C484, thereby to retain the first link 6| marked as busy to the finder switches of the various trunk circuits in the various groups having access thereto.

Continuing now with the operation of the common equipment second group 50, upon operating, the cutoi relay R640 also interrupts, at the contacts 642, the previously traced circuit for energizing the magnet M816, thereby positively to prevent further operation of the finder switch 5IF at this time, whereby the nder switch 5IF is arrested while the wipers thereof engage the contacts in the associated contact banks terminating the conductors C48I to C485, inclusive, extending to the rst link 6 I, as previously noted. Also the cutolT relay R640 completes, at'the contacts 643, a circuit, including the conductor C619, the contacts 8I5', 831, 8I1, the conductor C615 and the resistor 652, for energizing the-winding of the switch-through relay R860, whereby the latter relay operates. Upon operating, the switch through relay R860 completes, at the contacts 862', an obvious connection between the second marking conductor C502 and the chain conductor C823 extending to the second trunk circuit in the second group, thereby to render the other trunk circuits in the second group selectable via the second marking conductor C502 by the marker switches of the other links at this time.

Also when the lockout relay R8I0 operated it completed, at the contacts 8I4,` obvious multiple circuits for energizing the upper windings of the signal relay R160 and the supervisory relay R110, thereby to cause these relays to operate. Also the lockout relay R8I0 completed, at the contacts 8! I, an obvious holding circuit for energizing the lower winding of the signal relay R160, the latter relay being operated at this time. Upon operating, the signal relay R160 completes, at the contacts 163, an obvious circuit for energizing the winding of the signal slave relay R180,

thereby to causev the latter relay to operate. Upon operating, the signal slave relay R180 completes, at the contacts 18|, an obvious holding circuit, including the contacts 115, for energizing the lower winding of the supervisoryrelay R110.

Also when the cutoff relay R640 operatedit interrupted, at the contacts 642, the previously traced holding circuit for energizing the Vwinding of the lockout relay R810, thereby to cause the latter relay to restore. Upon restoring, the lockout relay R8I0 interrupts, at the contacts 8I1, the previously traced circuit for energizing the winding of the switch-through relay R860 and completes, at the contacts 8I8, an alternative holding circuit for energizing the winding of the switch-through relay R860 in series with the magnet M816. The last-mentioned circuit ex' tends from ground by'way of the contacts 18|,

864 and 866, the winding ofR860, the contacts"V v 602 of the repeating coil 600 and the contacts 606 of the talk key K606, for short-circuitng the winding of the ysignal relay R620 in the position equipment at the operator switchboard 3| in the distant exchange 30. Subsequently, when theV lockout relay R8I0 restored it inter--V rupted, at the contacts 8II, the above-traced path for short-circuiting the winding of the signal relay R620,whereby a series holding circuit substantially identical to that traced above" is completed for energizing the winding of the sig-s nal relay R620 and the lower Winding of the signal relay R160. When the series holding circuit for energizing the winding of the signal relay R620 and the lower winding of the signal relay R is completed the signal relay R620 operates and the signal relay R160 is retained in its operated position. Upon operating, the signal relay R620 completes, at the contacts 62|, an obvious circuit for illuminating the answer lamp L605 in the position equipment at the operator switchboard 3|, thereby to indicate to the operator thereat that a cally is waiting to be Y answered on the rst trunk second group 53."

Also, upon restoring, the lockout relay R8I0 interrupts, at the contacts 8I4, the'previously traced' multiple circuits for energizing the upper windings of the signal relay R160 and the supervisory relay R110. However, the latter relays are retained in their operated position at this time due to the previously traced holding circuits for energizing the lower windings thereof.` Also, upon restoring, the lockout relay R8I0 recompletes, at the contacts 8I8, the common point in the circuitsV for energizing the windings of the lockout relays in the other trunk circuits in the second group, thereby to render the other trunk circuits in the second group selectable over the second marking conductor C502 by the marker switches of the other links at this time. Also the lockout relay R8I0 interrupts, at the contacts 81| I', the previously traced circuit for ener-A gizing the winding of the timer relay R635 in the common equipment second group 50, thereby.

toncause the flatter yrelay :to restore. Upon -restoring, Ythetime'i .relay R635 interrupts., 'at the l dprevent.operation of thelatterrelay atthis time. Y

`Also, -upon operating, the vswitch-through `relay R860 completesrat thefcontacts 86| and 586,2, an obvious connection between the windings '193 and 194 fof the' repeating coil '190 and the line wipers 81| 1an-d 812 Lof `"the finder `switch 5|F; .and comfp'le'tes, atjthe ;c0ntacts-8.6'2, `a :circuit for energizing thef'winding-of the*battery reverse relay R150.

' The last-mentionedV circuit lextends from ground bywayfofthelcontacts312,332, 31| and 433, the winding :394 of-Jt'he repeating coil 390, the contacts 462, the -wiper 4.112 ofthe finder switch 4=|F and the' engaged :contact 'in .theassociated .contact bankQC482, the wiper 812 .of the nder switch 5g|F andthe engaged contact in the associated con-tactbank, the contacts 662, the winding 194 of the repeating coil 190, the contacts 833 and^-1|2 Vand the vvwinding .of R150Y to battery. When thus venergized 'the battery reverse relay R150 :operates to condition the'liney relay R1a|0 to supply `Areversed Ebattery 'over vthe 'first trunk second group .153, in .Ta :manner morezfully explained hereinafter.

the operator at ,the Yswitchboard 3| in the distant .exchange 3.0 observes the illuminated answerl lamp 13605 she answers the call o-n the first :trunk second lgroup .53 by operating the talk keyKl, vtherebyto interrupt, Yat the contacts 60Uthereof, the previously traced holding circuit forien'er'gizing .the winding 2of the 'signal .relay R620i-nseries with the lower winding .of the signal relay R160 Iorder .tolcause these 4'relays to restore. Also when the talk`keyK6106 isthus operated there is completed, .at 'the contacts 601 thereof, a'sriesbircuit for venergizing 'the winding of the supervisory relay R6 |10 and Athe upper L ing `of .'RgH), Athe contacts 601 of the talk key Kllthefwinding 60.2 ofthe repeating coil 600, the dial 1609,9 the line Aconductor 'C612 of the first trunk .53, the winding 192 of the :repeating coil 190, the contacts 161| fand '1.54 and the'upper winding lof R1|0 to battery. When this series circuit .is completed rthe Aline relay R1 0 operates; also `the supervisory relay R6|0 operates in View ofthe reverse direction Iof -the supply of battery current via the 4upperzand lower windings of the line relay Bl1|0 to the -linefconductors of the nrst trunk 5:3,-the supervisoryfreiay iR6|i0 being of thepolarized type. AUpon operating, the supervisory relay R6|10 completes, .at the contacts 6| I, an obvious Acircuit for illuminating the supervisoryilamp'fL604. -Upon operating, the line reY lay1R1f|0 completes, at the contacts 1|2, an obvi-ous .circuit for -energizi-ng the winding `o-f the hold :relay R120, thereby to :cause the -latter relay 'to .operate .and complete, at the contacts 1272, a :holding circuit :substantially A.identical to that previously traced for 4energizing the winding -of the :switch-through relay R860 :in series with the mag-net M816 iand an obvious multiple holding .circuit ysubstantially identical to that previously traced for energizing Vthe .lower vWinding of the supervisory relay R110. At .this poin'tI it is noted that, upon restoring, the .signal 'relay R160 interrupts, at the contacts 5163, the previously 'men-V tioned circuit :for-energizing the winding `of `the signal slave relay R180, thereby to cause the lat.- ter relay to restore shortly thereafter, the .signal slaverelay R180 being of the slow-to-release type. However, the signal .slave relay R180 .does r:not

, restore `until subsequent `to .the operation of the line relay R1|0 andthe hold relay R120, where-v by the supervisory relay R and the switch# through .relay R860 are retained in Vtheir operated positions.

.Also the .line Yrelay R1 |40 completes, at the contacts 1|2, a'circuit for energizing the winding of the'battery reverse relay R350 in the rst trunk circ-uit rst Vgroup 41|, the last-mentioned circuit extending from ground by way of the contacts 112 132, 114 .and 834, thefwind-ing 193 of the repeating coil 179,0, the contacts 86|, the line` wiper 81| "of the nder switch 5|F and the en; gaged contact in the associated contact bank, 048|, the line wiper 41| of the finder switch 4|=F and the engaged Contact in the associated contact bank, the contacts --46|, .the winding 393 of the repeating coil 390, the contacts 434 yand 313 and the winding of R350 to battery. When thus energized the battery reverse lrelay R350 operates in order to cause battery potential to be reversed over the rst trunk first group 43, in the manner` previously explained. At this time the upper andlower windings `of .the line relay R3|0 are energized in series with the winding of the supervisory relay R2|0 and the direction of battery supply over .therst .trunk 43 is such that the supervisory relay R2|0 operates, the latter relay being .of the polarized type .as previously noted. Upon operating, the supervisory relay R2|0 completes, at the `contacts .2||, the previously mentioned .circuit for illuminating the supervisory Ilamp .L204, thereby to indicate to the .operator .at the switchboard 2| .that the call has been vanswered by the .operator at the switchboard 3|.

.At .this time 4an established connection .is completed between the calling operator switchboard 2| in .the .distant exchange 20 .and the called operator switchboard ,3| in the distant exchange 30. Moreparticularlvthe position equipment at Y thevvcalling operator switchboard 2| vis `operatively connected by Way of the previously traced loop circuit, including the first trunk vfirst group 43 .and the windings 39| and 392 ofthe repeating coil .390 to the upper and lower windings of the line relay R3|0 in the rst trunk circuit first group 4|; the position equipment at the called operator switchboard 3| is operatively connected by way of the previously traced loop circuit, including the rst trunk second group 53 and the windings 1.9.| and 192 of the repeating coil 190 to the upper and lower windings of the line relay R1|0 in the rst trunk circuit second group 5|;

the Vwindings 393 and 394 of the repeating coil 39,0 in the `iirst trunk `circuit first group 4| are connected by way of the condenser 396 and thev contacts 46| and 4.62 to the line wipers 41| and 412 of the finder -switch 4|F; the windings `1.93 and 1.94 `of the repeating `coil in the first trunk circuit second group 5| are connected by way cf the condenser 196 and the contacts 86| and 852 tothe line wipers 81| and 812 of the finder switch 5| F; and the line conductors 048| and C402 extending to the -first link 6| -are terminated by the contacts engaged by the line wipers 41| and 412 of the nder switch 4IF, as well as by the contacts engaged by the line wipers 81| and 812 of the nder switch IF. Accordingly, at this time, the operator at the calling switchboard 2| in the distant exchange 20 may converse with the operator at the called switchboard 3| -in the distant exchange 30.

In the event the operator at the calling switch# board 2| in the distant exchange 20 should desire to resignal the operator at the called switchboard 3| in the distant exchange 30, this may be accomplished by operating the dial 209 in accordance with any digit, thereby to cause the line relay R3|0 in the iirst trunk circuit rst group 4| to follow the digit mentioned. Each time the line relay R3|0 restores and then reoperates it interrupts and then recompletes, at the contacts SI2, the previously-traced circuit for energizing the winding of the battery reverse relay R150 in the rst trunk circuit second group 5I, thereby to cause the latter relay to follow the impulses of the digit mentioned. Each time the battery reverse relay R150 restores and then reoperates it effects the reversal of battery potential over the line conductors of the first trunk second group 53, whereby the supervisory relay R6I 0 follows the impulses of the digit mentioned, the supervisory relay R6I0 being of the polarized type, as previously noted. Each time the supervisory relay R6I0 restores'and then reoperates it interrupts and then recompletes, at the contacts 6II, the previously mentioned circuit forl illuminating the supervisory lamp L6M, whereby the supervisory lamp L604 is flashed in accordance with the digit mentioned. The flashing of the supervisory lamp L604 in accordance -with the digit mentioned attracts the attention of the operator at the called switchboard 3| in the distant exchange 30. i

In the event the operator at thecalled switchboard 3| in the distant exchange 30 shouldV desire to resignal the operator at the calling switchboard 2| in the distant exchange 20, this may b-e accomplished by operating the dial 609 in accordance with any digit, thereby to cause the line relay R1! Il in the rst trunk circuit second group 5I to follow the digit mentioned. Each time the line relay R1I0 restores and then reoperates it interrupts and then recompletes, at the contacts 1I2, the previously traced circuit Vfor energizing the winding of the battery reverse relay R350 in the rst trunk circuit first' group 4I, thereby to cause the latter relay to follow the impulses of the digit mentioned. Each time the battery reverse relay R350 restores and then reoperates it eiects the reversal of battery potential over the line conductors of the first trunk rst group 43, whereby thesupervisory relay R2|0 follows the impulses of the digit mentioned, the supervisory relay R2I0 being of the polarized type, as previously noted. Each timethe supervisory relay R2I0 restoresv and then reoperates it interrupts and then recompletes, at the contacts 2| I. the previously mentioned circuit for illuminating the supervisory lamp L204, whereby the supervisory lamp L204 is flashed in accordance with ithe digit mentioned. The ilashing of the supervisory lamp L204 in accordance with the digit mentioned at-f tracts the attention of the operator at the calling switchboard 2| in the distant exchange 20l 'Ihe release of the established connection between the calling operator switchboard 2| in the distant exchange 20 and the called operator switchboard 3| in the distant exchange 30 mayy be initiated at either of the switchboards mentioned. The operator at the calling switchboard 2| may initiate the release of the established connection by restoring the talk key K206` in order to eiiect the restoration of the supervisory relay R2 I0 and the line relay R3|0, in an obvious manner; and, upon restoring, the line relay R3|0 interrupts, at the contacts 3|2, the previously traced circuit for energizing the winding of the battery reverse relay R150, thereby to cause the latter relay to restore and eiTect the restoration of the supervisory relay R6 I 0, whereby the supervisory lamp L504 is extinguished in order to in dicate to the operator at the called switchboard 3| that' the release of the established connection has been initiated by the operator at the calling switchboard 2|. On the other hand,the operator at the called switchboard 3| may initiate the re'- lease of the established connection by restoring the talk key K606 in order to effect the restoration of the supervisory relay R6I0 and the line relay R1I0, in an obvious manner; and, upon restoring. the line relay R1 I 0 interrupts, at the contacts 1I2, the previously traced circuit for energizing the winding of the battery reverse relay R350, thereby to cause the latter relay to restore and effect the restoration of the supervisory relay R2I0, whereby the supervisory lamp L204 is extinguished in order to indicate to the operator at the calling switchboard 2| that the release of the established connection has been initiated by the operator at the called switchboard 3|. When the operator at the called operator switchboard 3| receives the release supervision indicated above, she restores the talk key K606; and when the operator at the calling operator switchboard 2| receives the release supervision indicated above, she restores the talk key K206. Y

vAlso, upon restoring, the line. relay R3|0 in the irstl trunk circuit first group 4I interrupts, at the contacts 3|2, the Fpreviously mentioned circuit for energizing the winding of the hold relay R320, thereby to cause the latter relay to restore shortly thereafter. Upon restoring, the hold relay R320 interrupts, at the contacts 322,

the previously traced holding circuit for energizing the winding of the switch-through relay R460, thereby to cause the latter relay to restore; Upon restoring, the switch-through relay-R460 interrupts, at the contacts 469, the previously traced circuit for energizing'the winding of the step relay R450, thereby to cause the latter relay to restore. Further, the switch-through relay R460 interrupts, at the contacts 46| and 462,v the previously traced connection between the repeating coil 390 and the linevwipers 41| and 412 of the finder switch 4 IF', thereby to interrupt the connection to the line conductors C48! and C482 extending to the rst link 6I. Further the switch-through relay R460 recompletes, at the contacts 453', the previously'traced connection between the first marking conductor C50| and the winding of the lockout relay R4I0, thereby to mark the first trunk circuit iirst group 4| asuse.

,Also when the line relay R3 0 in the first trunk circuit vfirst group k4| restores it interrupts, at the contacts '3|'4, the previously traced `circuit for energizing the winding of kthe pulse relay R520 inthe rst link 6|, thereby to cause the latter relayto restore and eiect the restoration of the hold relay R530 shortly thereafter. Upon restoring, the hold relay R530 interrupts, at the contacts 532, the previously traced holding circuit for energizing the lower winding of the release relay R560, thereby to 'cause the latter relay to restore. Also, upon restoring, the hold relay R530 completes, at the contacts 535, the previously traced circuit for energizing the release magnet M581, thereby to cause the latter magnet to operate and release the wipers noted of the marker switch 580. When the marker switch 580 is thusv released the set of switch springs S584 is operated, thereby to interrupt, at -the contacts 586 thereof, the previously traced circuit for energizing the release magnet M581 inorder to cause the latter magnet to restore. Further the hold relay R530 interrupts, at the contacts 533, the previously mentioned path for applying ground potential to the control conductor C484, whereby the first link 6| is marked as idle to the nder switches of the various'trunk circuits in the various Y groups having access thereto. At this time the rst link 6| is completely released and available for further use.

Also, upon restoring, the line relay R1|0 in the Iirst trunk circuit second group 5| interrupts,

at the contacts 1|2, the previously mentionedV circuit for energizing the winding of the hold relay R120, thereby to Acause the latter relay to restore shortly thereafter. Upon restoring, the hold relay R120 interrupts, at the contacts 122, the previously traced holding circuit for ener-- gizing the windingof the switch-through relay R860, thereby to cause the latter relay to restore. Upon restoring, the switch-through relay R860 interrupts, at the contacts 86.9, the previously traced `circuit for venergizing the winding of the step relay R850, thereby to cause the latter relay Y to restore. Further the switch-through relay R860 interrupts, at the. contacts 86| and l862, the -previously traced connection between the repeating lcoil 190 and the line wipers .81| and 812 of the finder switch A5 IF, thereby to interrupt the connection to the line conductors C48| and C482 extending to the rst link 6|. Further the switch-through relay R860 recompletes., at the y contacts 8.63', the previously traced connection between the second marking conductor C502 and the winding of the lockout relay R8|0, thereby to mark the first trunk circuit second group 5| as selectable via the second lmarking conductor f C502 by the marker switches of the various links.

Further the hold relayR120 interrupts, .at the contacts 122, the previously traced holding circuit for energizing the vlower winding of the supervisory relay R110, thereby to cause Vthe latter relay to restore. At this time the first trunk circuit second group 5| is'completely released and available for further use.

In view of the foregoing explanation of the mode of operation of the vfirst trunk circuit rst group 4|` in conjunction with the first link 6| and the first trunk circuit second group 5| to extend `a connection from the calling operator switchboard 2| in the distant exchange 20 to the called operator switchboard 3| in the distant exchange via the rst tru-nk first group 43 and the 4first trunk second -g-roup 53, ,-it `will be understood that any-one of thetrunk circuits in lthe first group is operative in conjunction with any one of the links and any one of the trunk circuits in the second group, in a substantially identical manner, to extend a connection from the calling operator switchboard 2| in the distant exchange 20 to the called operator switchboard 3| in the distant exchange 30 via the corresponding `trunk in the iirst group andthe corresponding trunk in the second group. Also, any one of the trunk circuits in any one of the groups is operative in conjunction with 4any one of the links and any one of the trunk circuits in any other of the groups, in .a substantially identical manner, to extend a connection from the calling operator Aswitchboard in the corresponding one distant exchange vto the called operator switchboard in the corresponding lother distant exchange via the corresponding trunk in the one group and the corresponding trunk in the other group. f

YIn the foregoing explanationof the mode of operation of the first trunk circuit Vsecond group 5| in conjunction with the common equipment second group in order to 4arrest operation of the nder switch 5|F of the rst trunk circuit 5|, when the conductors C48| to C485, inclusive, extending to the rst link 46| are selected by the Wipers noted of the finder switch '5|F, it was assumed that this operation took place inY avery short interval of time following the operation of the timer relay R635 in the common equipment second groupV 50 and prior to the operation of the timer relay R630. However, it may occur that the nder switch 5|E1 operates in the man- Vner previously explained, but is unable to nd the marking conductor YC483 extending to the rst link 6| in order t0 effect operation of the cutoff relay R640 in the common equipment second group 50, in the manner previously explained. In this event, a predetermined time interval 'after the operation of the timer relay R635 and after the finder switch 5|l1` has had ample time to iind the conductors C48| to C485, inclusive, extending to the rst link 6|, the timer relay R630 operates. As previously explained, upon operating, the timer relay R635 ysets its armature into vibration, whereby the circuit for energizing the winding of the timer relay R630 is completed intermittently at the contacts 631, and the timer relay R630 is of the slow-to-operate type. Upon operating, the timer relay R630 interrupts, at the contacts 63|, the previously traced circuit for energizing the magnet M816, thereby positively to arrest further operation of the finder switch 5|F at this time. Also the timer relay R630 interrupts, at the contacts 63|, the previously traced holding circuit for energizing the winding of the lockout relay R8|0 inthe first trunk circuit second group l5| in order to cause the latter relay to restore.

Upon restoring, the lockout relay R8|0eiects Vthe release of the rst trunk circuit 5| inthe first trunk circuit second group 5| is not initiated .Y and the first link 6| is locked out of service.

Accordingly, at this time, the connection extended, from the calling operator switchboard '2| in 

